Ignition coils

ABSTRACT

An ignition coil having a hollow casing closed at one end by an insulating cap which carries the high tension output terminal of the coil. The conductive core is housed within the casing and electrically connected to the core is one end of the secondary winding of the coil which encircles the core, the core being also electrically connected to the high tension output terminal. A primary winding also encircles the core and a conductive member is spaced from the core by the insulating support member. This conductive member defines with the core a capacitor the dielectric of which is the material of the support member and a terminal is provided on the cap of the ignition coil and electrically connected to the conductive member so that this terminal and the high tension output terminal constitute the terminals of the capacitor.

United States Patent Hillyard June 26, 1973 IGNITION COILS Primary Examiner-Thomas J. Kozma 75 Inventor: Peter ThomasIIillyard,So|ihull, Ammekloh Hmman, stem at England [73] Assignee: Joseph Lucas (Industries) Limited, [57] ABSTRACT Birmingham, England An ignition coil having a hollow casing closed at one [22] Filed Sept 15 1972 end by an insulating cap which carries the high tension output terminal of the coil. The conductive core is housed within the casing and electrically connected to the core is one end of the secondary winding of the coil which encircles the core, the core being also electri- [30] Foreign Apphcaumi Prlomy Data cally connected to the high tension output terminal. A Sept. 15, 197i Great Bl'ltaln 42,905/7] p y winding also encircles the Core d a Conduc tive member is spaced from the core by the insulating [52] US. Cl 3l7/l57.62, 336/69, 336/92 Support member This conductive member defines with [51] IlIt. Cl. H01 the core a Capacitor the dielectric of which is the mate [58] Fleld of Search 336/69, 84, 90, 92, rial of the pp member and a terminal is provided 317/1516 l57'62 on the cap of the ignition coil and electrically connected to the conductive member so that this terminal [56] References cued and the high tension output terminal constitute the ter- UNITED ST T S PATENTS minals of the capacitor.

3,566,202 2/1971 Carr 3l7/l57.62 1,946,631 2 1934 Loudon 3l7/l57.62 3 Clams 2 D'awmg F'gures 1,312,497 8/1919 Cavanagh 3l7/lS7.62

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IGNITION COILS This invention relates to ignition coils for internal combustion engine ignition systems and has for its object to provide an ignition coil in a form suitable for use in conjunction with fault diagnosing equipment.

An ignition coil according to the invention includes, a hollow casing closed at one end by an insulating cap carrying the high tension output terminal of the coil, a conductive core within the casing and electrically connected to said high tension terminal, an insulating support member engaging one end of said core, primary and secondary windings encircling said core with one end of the secondary winding electrically connected to the core, a conductive member spaced from said core by said insulating support member said conductive member defining with the core a capacitor the dielectric of which is the material of said support member, and a terminal on the cap of the ignition coil electrically connected to said conductive member so that said terminal and said high tension output terminal constitute the terminals of the said capacitor.

Preferably said conductive member is a metal plate interposed between the support member and a closed end of the casing opposite said cap.

Conveniently the casing is conductive and said conductive member is insulated therefrom, the member and the casing defining a second capacitor.

In the accompanying drawings FIG. 1 is a diagrammatic representation, partly in section of an ignition coil in accordance with one example of the invention, and

FIG. 2 is a circuit diagram illustrating the way in which the coil can be used in diagnostic equipment.

Referring first to FIG. 1 of the drawings, the ignition coil includes a hollow cylindrical metal casing 11 closed at one end by an integral base 12, and closed at its other end by a moulded synthetic resin cap 13. The open end of the casing 11 is spun over to grip the cap 13. The cap 13 carries a high tension output terminal 14 together with the usual pair of low tension terminals (not shown). Additionally, the cap carries a further terminal 15 connected by way of a conductive lead 16 to a metal plate 17 positioned adjacent the base 12. The plate 17 is spaced from the base 12 by an insulating disc 18, and trapping the plate 17 against the disc 18 is a hollow insulating support member 19 moulded in glass.

Extending between the support member 19, and the cap 13 and received at one end in the cap 13 and at its other end in the support member 19 is a laminated conductive core 21 electrically connected at its one end to the high tension terminal 13. The core 21 extends through a tubular paper former upon which are wound the secondary and primary windings of the ignition coil. In the usual manner, one end of the 22a, 22b secondary winding is electrically connected to the core 21, while the other end of the secondary winding and one end of the primary winding are electrically connected to one of said pair of terminals on the cap 13, the other end.

of the primary winding being connected to the other of said terminals on the cap 13.

The core 21 and the plate 17 are spaced apart by the base region of the glass support member 19, and the core 21 and the plate 17 define a capacitor 23 (FIG. 2) the dielectric of which is the glass base of the member 19. The high tension terminal 14 constitutes one terminal of this capacitor while the terminal 15 provided on the cap 13 constitutes the other terminal of the capacitor.

The support member 19 could be formed from materials other than glass provided they exhibit the desired dielectric and insulating properties. Phenolic resins have been used and are suitable for some applications even though their permittivity varies with temperature to a larger degree than glass.

In the conventional manner the inner surface of the casing of the ignition coil is provided with a paper sleeve which separates an inner iron sleeve from the casing 1 1. In the normal manner the casing is filled with oil.

The reason for the provision of the capacitor 23 in the ignition coil is best understood with reference to FIG. 2 which shows the secondary winding 22a of the ignition coil with its ends connected in the way described above to the high tension terminal 14 and the terminal E of the ignition coil respectively the terminal E being connected to earth through a low impedance path in use. The coil produces an alternating output having a voltage of the order of 30,000 volts, and if the vehicle on which the coil is employed is to be tested using automatic diagnostic equipment of the kind which tests various parts of the vehicle for faults, then it is necessary to step down this voltage, which can be accomplished readily by providing a pair of capacitors 23 and 24 in series across the winding 22a, and taking a voltage from the junction of the capacitors 23 and 24. Typical values for the capacitors 23 and 24 would be 5 p.f. and 5,000 p.f. respectively, giving a voltage between the junction of the capacitors and the terminal E of 30 volts. With the arrangement described, the terminal at the junction of the capacitors 23 and 24 is the terminal 15 with the capacitor 23 within the ignition coil constituted by the core 21, the plate 17 and the support 19. The capacitor 24 is a separate capacitor connected between the terminal 15 and the terminal E externally of the coil, but it is to be noted that since the casing 11 of the coil is, in use, at earth potential then the plate 17 and the base 12 define a capacitor in parallel with the capacitor 24 and so the capacitance of the capacitor 24 is chosen accordingly bearing in mind to total capacitance required between the terminals E and 15.

What we claim is:

1. An ignition coil, for an internal combustion engine ignition system, comprising a hollow casing closed at one end by an insulating cap carrying the high tension output terminal of the coil, a conductive core within the casing and electrically connected to said high tension terminal, an insulating support member engaging one end of said core, primary and secondary windings, encircling said core with one end of the secondary winding electrically connected to the core, a conductive member spaced from said core by said insulating support member said conductive member defining with the core a capacitor the dielectric of which is the material of said support member, and, a terminal on the cap of the ignition coil electrically connected to said conductive member so that said terminal and said high tension output terminal constitute the terminals of the said capacitor.

2. An ignition coil as claimed in claim 1 wherein said conductive member is a metal plate interposed between the support member and a closed end of the easing opposite said cap.

3. An ignition coil as claimed in claim 1 or claim 2 wherein the casing is conductive and said conductive member is insulated therefrom, the member and the casing defining a second capacitor. 

1. An ignition coil, for an internal combustion engine ignition system, comprising a hollow casing closed at one end by an insulating cap carrying the high tension output terminal of the coil, a conductive core within the casing and electrically connected to said high tension terminal, an insulating support member engaging one end of said core, primary and secondary windings, encircling said core with one end of the secondary winding electrically connected to the core, a conductive member spaced from said core by said insulating support member said conductive member defining with the core a capacitor the dielectric of which is the material of said support member, and, a terminal on the cap of the ignition coil electrically connected to said conductive member so that said terminal and said high tension output terminal constitute the terminals of the said capacitor.
 2. An ignition coil as clAimed in claim 1 wherein said conductive member is a metal plate interposed between the support member and a closed end of the casing opposite said cap.
 3. An ignition coil as claimed in claim 1 or claim 2 wherein the casing is conductive and said conductive member is insulated therefrom, the member and the casing defining a second capacitor. 